The review, led by Rod Taylor of the Peninsula College of Medicine and Dentistry at Exeter University, looked at seven studies, which examined almost 6500 participants.

They found while sodium reduction did produce a small blood pressure decline, there was insufficient evidence to determine whether this reduction of salt intake increased or decreased cardiovascular mortality.

"The people in the trials we analysed only reduced their salt intake by a moderate amount, so the effect on blood pressure and heart disease was not large," says Taylor.

They say a future study including 18,000 participants would be needed to draw firmer conclusions.

"With governments setting ever lower targets for salt intake and food manufacturers working to remove it from their products, it's really important that we do some large research trials to get a full understanding of the benefits and risks of reducing salt intake," says Taylor.

Cautious response

Robert Walker from the School of Medicine at the University of Otago in New Zealand says lowering salt intake can reduce blood pressure.

"However, blood pressure is not the only cardiovascular risk and therefore it has to be seen in the global context of reducing risk not as the sole intervention to reduce heart attacks," he says.

Delvina Gorton from the Heart Foundation says they will continue to advise people to reduce their salt intake.

"Reduced risk ratios suggested a beneficial effect from moderate salt reduction but the sample size was too small for the trend to be conclusive," says Delvina.

High blood pressure, or hypertension, is a major risk factor for cardiovascular diseases such as heart failure, heart attacks and stroke, which are the world's number one killers.